Self contained breathing apparatus is well known in the art and is used in many environments by fire fighters, haz-mat persons and the like who might be exposed to noxious atmospheres. Such breathing apparatus generally includes a supply of pressurized air originally at a relatively high pressure, and regulator devices to reduce the pressurized air to a lower level. The air at the lower pressure is made available to a user, often in a face mask or hood or similar device. The regulator devices may be fairly complex in some instances in having first and second stage regulators. Such regulator devices may deliver air in response to a user's inhalation. Also, such regulator devices may maintain a pressure higher than ambient pressure in the user's face mask or hood so as to prevent entry of noxious gases into the breathing system. All such systems, however, are subject to the common occurrence that being self contained, the supply of air will eventually be depleted and it is advantageous to provide a signal to the user of this impending situation.
Many forms of apparatus have been devised to provide such a signal to the user. Prior arrangements have included vibrating alarm devices, whistles, visual indicators and the like which are operative upon a change in fluid pressure within the regulator system to signal the user of a certain condition of the system related to a relatively low supply of pressurized breathing air.
Examples of such a system are shown in prior patent, U.S. Pat. No. 3,957,044 and in co-pending application, International Application No. PCT/US98/06158. In both of these systems a first stage regulator is used to supply air to a second stage regulator, the latter mounted on a user's face mask, for example. The first stage regulator supplies air at a first pressure level until the pressure level of the air supply drops to a lower level, indicating an approach to depletion of the air supply. This condition is recognized in the regulator system, in one instance by use of dual first regulator valves and in the other by use of a transfer valve which modifies the action of the first regulator valve. In both systems the outlet of the first regulator valve is raised to a second higher pressure for application to the second regulator valve.
This second higher pressure is recognized in these systems in a sensing chamber which includes a moveable piston which is exposed to the outlet of the first regulator valve. The pressure on the piston acts against a spring bias to close electrical contacts as the bias is overcome. A signal lamp such as an LED may be lighted or alternative signals employed, such as whistles, sirens, on/off indicators and the like. In these systems however, only a single level of air supply pressure is utilized to initiate the alarm signal, typically being when the air pressure level has dropped to about one-fourth of its initial pressure level. While this is a tried and proven technique for signaling, there is still some variability in the timing of the remaining air supply which is dependent upon several factors, including among others, the integrity of the entire air supply system, the form of mask or hood being used, and the physical breathing rates or volumes of the user. Thus, the availability of breathing air to the user is variable in time and it is the available time which is important in the decision-making process of the user.
This factor has been recognized in the past and solutions have been indicated. Thus, in my co-pending application, previously referenced, a clock device or timer is indicated which is triggered upon sensing the higher pressure level applied to the second stage regulator. The timer can then provide signals at a periodic interval or can change the flash rate of LEDs or the like, based upon a pre-assumed time out. However, such a system still does not accommodate the actual conditions occurring in the regulator system which are variable among users, the system parameters, the environment and the like as previously described.
Thus, there is a need for a self contained breathing apparatus that provides a user with an indication of impending depletion of the air supply, which provides plural indications and which is more accurate than prior systems.